The amount of electrostatic charge on an object can be rapidly altered as a result of an electrostatic discharge (ESD) event. An ESD event can alter the electrical characteristics of circuitry including semiconductor components so as to degrade or destroy the components. The voltage potential from accumulated charge may exceed the component's breakdown threshold and lead to damage from excessive voltage or damage from the resulting discharge currents. As electrical devices and components have become smaller, they have become more susceptible to harm from ESD events.
ESD events impact production yields, product quality, and product reliability. ESD events can occur throughout manufacturing, testing, shipping, handling, or use of a product. Component damage can occur due to a discharge or from the accumulation of charge. Ample opportunities for an ESD event arise during the manufacture and use of electronic circuitry including integrated circuits.
ESD mitigation approaches are implemented to improve or ensure production yields, product quality, or product reliability. With respect to integrated circuits, ESD protection circuitry is incorporated into the integrated circuits to protect the core of the integrated circuit from ESD events that might occur during manufacture, testing, and use. Integrated circuit ESD protection typically shunts current on integrated circuit pads or voltage rails through a device more suitable for carrying larger currents than the core of the integrated circuit.
One ESD protection circuit architecture uses a shunt having a trigger with a short time constant. The short time constant enables the ESD protection circuitry to better distinguish between normal transient events such as a power-up and fast events such as ESD, to avoid undue interference with transient operations that are part of the normal operation of the integrated circuit. The smaller time constant can cause the ESD protection circuitry to inadequately dissipate the charge or to take an undesirably long time to dissipate the charge.
Another ESD protection circuit architecture uses a shunt having a trigger with a long time constant. The long time constant can result in a more complete dissipation of the charge or a faster dissipation of the charge. One disadvantage of the long time constant, however, is that the ESD protection circuit may be less capable of consistently and reliably distinguishing an ESD event from other transient events such as a power-up. Another disadvantage of typical long time constant shunt designs is the relatively large semiconductor die area used to implement the long time constant.